As a conventional binding device serving as the background of this invention, there is a binding device disclosed in, Japanese Patent Application Laid-Open No. 2001-277770.
This binding device includes: an upper plate; a pair of rotational leafs supported by the upper plate; a plurality of rings attached to the rotational leafs and movable together with the rotational leafs; and at least one pivotable operation lever for moving the rotational leafs from a first position where the rings have been closed to a second position where the rings have been opened, where the operation lever has a tab at an upper portion thereof including a groove, and further has a cushion member extending over the tab and surrounding the tab, and secured to the operation lever, and the cushion member has a tongue portion received and secured in the groove.
The pair of rotational leafs are supported by a curved upper plate 12. The curved upper plate applies a biasing force to the rotational leafs, so that the rotational leafs move beyond a center. The plurality of ring members are secured to the rotational leafs, and are engaged with corresponding holes of a material sheet held by a ring binder.
The operating lever is arranged at each end portion of the curved upper plate and operates the rotation leafs to open/close the ring members.